The present invention relates to a slow release urea fertilizer composition and a process for the preparation of the said composition. More particularly, the invention relates to a slow release urea fertilizer composition and process for the preparation of the said composition wherein coating of a nitrogenous fertilizer with essential oils or their derivatives acts as a cheap and potential urease/nitrification inhibitor.
Nitrogen is considered to be one of the most vital agricultural inputs in crop production. It is estimated that the present global consumption of fertilizer nitrogen is of the order of 77 Tg annually which is likely to be increased to 144 Tg by 2000 AD. The present consumption of fertilizer N in India, of which urea comprises 80%, is about 9.5 million tons, which is estimated to be enhanced to about 14 million tons by the end of this century to produce about 225 million tons food grains. Fertilizer N use efficiency seldom exceeds 50% in arable crops; the utilization efficiency is even less under rainfed conditions, It is further less in paddy (20-30%) where fertilizer losses are greatest. In addition to the large amount of fertilizer N needed, high cost involved in their production or purchase also need to be considered. Thus, efficient use of fertilizer N is necessary, suggesting that regulation of N transformations in soil have a major role to play.
Fertilizer urea when applied to soil is hydrolyzed by enzyme urease to form NH4 and finally to NO3 which is prone to losses through denitrification and leaching. The NH4 is subjected to losses through volatilization. Apart from increasing the cost of cultivation in agriculture, N loss through leaching as well as in gaseous forms has direct concern in environmental degradation. As a consequence of leaching NO3 concentration in ground water has been increasing at an alarming rate. Any technique that can restrict or retard these processes would reduce the loss of N. The present invention deals with finding strategies for retarding urea transformation and nitrification for a higher fertilizer N use efficiency.
Lot of research works have been done on management strategies for improving utilization efficiency of nitrogenous fertilizers specially urea which accounts for about 80% consumption of the total nitrogenous fertilizers. A number of review articles have dealt with the environmental, chemical and physical factors affecting the hydrolysis of urea in soil (Gould et al 1986, Adv. Akgron. 40:209-238). Urease inhibitors and methods of controlling urea transformation in soil were thoroughly reviewed by several workers (Sahrawat 1980, Plant Soil 57:335-252, Mulvaney and Bremner 198, Soil Biol. Biochem. 5:153-190). Review of Martens and Bremner (1984) gives an account of inhibitors like phosphorodiamidates and phosphorotriamides which have been found effective in several conditions (Soil Sci. Soc. Am. J. 48:302-305). Several sulfhydryl reagents, hydroquinones, catechol, P-benzoquinones, dihydric phenols. aminocresol have been found to restrict hydrolysis of urea (Rodgers, 1984, Plant Soil 79:115-158). The efficacy of hydroxamic acids has been studied as urease inhibitors but it has not been found very effective for a long period (Pugh and Waid 1969, Soil Biol Biochem. 1:195-206).
Compounds that have structural similarities to urea inhibit urease by competing the same active site on the enzyme. Thio-urea, methyl urea and the substituted phenylurease are known inhibitors of urease. Ash worth et al (1980) measured urea hydrolysis and nitrification inhibition in soil by a number of xanthalates (Soil Sci. Soc. Am. J. 44:1247-1251). Neither the substituted urease nor the xanthalates provide sufficient inhibition of soil urease to be of practical agricultural value. Several phosphoroamide class of compounds have been tested but only few have been examined as potential under some specific environmental and edaphic conditions. Urea has been coated Nvitli resin, plastic shellac, silica and sulphur and impregnated with petroleum wax in order to retard the dissolution of urea in the soil. Sulphur coated urea has been found most effective among the coated fertilizers but its main disadvantages are higher cost than soluble nitrogenous fertilizers and soil acidification due to formation of H2SO4.
Another slow release urea fertilizer is produced by polymerization or condensation of urea with an aldehyde. Crotonylidinediurea ((CDU) and isobuitlidene diurea (IBDU) are zo slow release nitrogen sources produced by the condensation of two urea and two aldehyde molecules (Gould et al 1986, Adv.Agron. 40:209-238). IBDU have been found superior to SCU under field conditions.
In order to reduce volatilization of ammonia urea has been mixed with other chemicals such as ammonium polyphosphate, phosphoric, boric and nitric acid (Mudrock and Frye, 1985, Adv. Agron. 77:630-633). Similarly urea-thiourea mixtures placed in either bands or pellets have been used to retard the transformation of urea in the soil. Thiourea is both a weak urease and nitrification inhibitor; alone it has been utilized as a slowly available source of both sulphur and nitrogen (Malhi and Soper 1981, Agron. J. 73:991-995). Nitrification inhibitors are the materials which restrict the microbiological oxidation of armonium to nitrate thereby reducing the loss of N by leaching and denitrification. The literature on nitrification inhibitors is very extensive (Prasad et al. 1971, Adv. Agron. 23:337-383, Sahrawat and Keeney 1985, Commu. Soil Sci. Pl. Anal. 16:517-524; Sahrawat 1989, Adv. Agron. 42:279-302). These reviews cover various aspects of the effects of nitrification inhibitors on retardation of nitrification in soil and crop production. In a recent revies Prasad and Power (1995) provides an overview of the status on the use of nitrification inhibitors in relation to productivity, human and animal health and the environment (Adv. Agron. 54:234-281). The interest in nitrification inhibitors followed the development of nitrapyrin (2-chlor-6-(trichloromethyl pyridine) by the DOW chemical company USA as an effective inhibitor of nitrificanon. Subsequently a series of chemicals viz. BHC. sodium azide sodium chlorate. dicyanodiamide (DCD), thiourea AM (2-amino-4 chloro-6 methyl prindine), ATC (4 amino-1,2,4 tnazole), N-serve etc. have been identified as nitrification inhibitors (Sahrawat et al 1989, Adv. Agrron. 42:279-309). Use of most of these chemicals have been restricted to academic experimental stage because of their difficult availability, higher cost and adverse effect on soil processes. Allelochemic inhibition of the process of mineralization and nitrification has been reported to occur in many ecosystem (White 1986, Biol. Fert. Soil 2:97-104). Polyphenols particularly tannins and organics which are water soluble and volatile are presumed to have N-inhibitory properties: Karanjin from Karanj (Pongamia glabra) and tea waste have been reported to retard nitrification (Sahrawat et al 1989, Adv. Agron. 42:279-309). Medicinal plant products like Pyrethrum flower (Crvsanthaxium cinerariefolium) waste have also been found to have this property (Ram et al 1993, Indian Soc. Soil Sci. 41:176-177).
Researches being carried out in India on inhibitors have been reviewed by Prasad et al (1971, Adv. Agron. 23:337-383 and Sahrawat et al 1989, Adv. Agron. 42:279-309). Lac-coated urea (LCU) has been effectively evaluated by Bhowmik (1980, Fert. News 25:17-19). Dissolution rate of LCU has been found to be more or less equal to sulphur coated urea. The pioneering works in India on this aspect include that of Prasad and Rajale (1972, Soil Biol Biochem. 4:450-457), and Sahrawat et al (1989, Adv. Agron, 42:279-309), who reported inhibitory properties in Karanj (Pongamia glabra) and Neem (Azadirachta indica). Neem cake coated urea besides having slow releasing properties had additional beneficial effect in inhibiting nitrification in soil.
The main objective of the present invention is the preparation of a slow release urea fertilizer composition and a process for the preparation of the said composition which obviates the drawbacks of the previous inventions. Another objective of the present invention is to develop a cheap and eco-friendly urease and nitrification inhibitor. The materials being easily decomposable are expected to leave no adverse influence in soil.
In accordance with the above objectives, the invention provides a novel composition for a slow release nitrogenous fertilizer comprising about 0.5-1% of an inert material, and 0.5-1% of essential oil or their derivatives on w/w basis. The invention also provides a process for the preparation of the composition of a slow release nitrogenous fertilizer comprising the steps of coating a nitrogenous fertilizer with an inert material, air drying the coated fertilizer, further coating the said coated fertilizer with an essential oil or its derivatives and drying the coated fertilizer for about 24 hours.
The present invention comprises of development of urease and nitrification inhibitors from some essential oils and their derivatives viz. Mentha spicata oil, denentholosized oil (DMO) and terpene coated with nitrogenous fertilizer (urea) at 0.5-1.0% on w/w basis. At 0.5% level of application, these three natural products retard nitrification to an extent of 24-31% over control (no coating material) as against 32% with DCD as the standard reference. The corresponding retardation at 1% level of application ranges between 33-37%; DCD retards nitrification by 44% over control. The urease activity retarted by 15-29% over control (urea alone) at 0.5% level of application and 26-34% over control at 1.0% level of application of the materials. Nitrosomonas activities decreased by 9-51% and Nitrobactor activities by 68-89% over control, with coating of urea with the natural products. Consequently coating urea with natural products increased apparent nitrogen recovery to 48-56% as against 29% with urea alone (no coating material) and 48% with DCD.
Accordingly, the present invention provides a slow release urea fertilizer composition and a process for the preparation of the said composition which comprises about 0.5 to 1.0% of an inert material such as castor oil, about 0.5 to 1.0% of essential oil or their derivatives and the balance being a nitrogeneous fertilizer such as urea on w/w basis.
In an embodiment of the invention the process for the preparation of slow release fertilizer composition comprises coating a nitrogeneous fertilizer such as urea with an inert material such as castor oil and air drying the said coated nitrogeneous fertilizer for 24 hours followed by further coating the said castor oil coated fertilizer with an essential oil or its derivatives and air drying the said coated fertilizer for about 24 hours.
In another embodiment of the invention wherein essential oils or their derivatives used for coating nitrogeneous fertilizers act as xe2x80x9curease and nitrificationxe2x80x9d inhibitors.
In yet another embodiment, inert material such as castor oil is used for coating the nitroaeneous fertilizer as a fixative material.
In still another embodiment of the present invention the essential oils and their derivatives used may be selected from Mentha arvensis, Mentha spicata, Mentha piperita, Mentha citrata terpene, DMO etc.